This invention relates to magnetic recording media, and more particularly, to magnetic recording media having a magnetic layer of the continuous metal thin film type as well as a method for making same.
Among magnetic recording media for use in video, audio and other applications, active research and development work has been made on magnetic recording media, usually magnetic tapes having a magnetic layer in the form of a continuous thin film because of the compactness of a roll of tape.
The preferred magnetic layers for such continuous film type media are deposited films of Co, Co-Ni, Co-O, Co-Ni-O and similar systems formed by the so-called oblique incidence evaporation process in which cobalt and optional elements are evaporated and directed at a predetermined angle with respect to the normal to the substrate because such evaporated films exhibit superior characteristics. The evaporated magnetic layers are, however, prone to oxidation with time and hence rusting, incurring many performance losses including reduced output and runnability (that is, the durability of tape which travels in frictional contact with rigid members in a video equipment). The media suffer from poor head contact and output variations due to curling or cupping thereof.
Great efforts have been made to overcome the problem. One typical attempt is the provision of a plasma-polymerized film on the magnetic layer as disclosed in Japanese Patent Application Kokai Nos. 58-8828, 58-8829, 58-102330, 58-194131, 59-72653, 59-154641, 59-154643, and 59-160828. It is also proposed to oxidize the surface of the magnetic layer to produce a metal oxide region and forming a plasma-polymerized film thereon as disclosed in Japanese Patent Application Kokai No. 59-171028. These attempts are successful in improving the corrosion resistance and durability, but fail to provide fully satisfactory results in minimizing the output variation of the medium due to curling or cupping thereof. There is a need for further improvement in this respect.